Characterization of defensin (Tfgd2) from Trigonella foenum-graecum

Abstract

Defensins are small cysteine-rich peptides with a size of 5-10 kDa, and some of them exhibit antifungal activity. We have cloned and sequenced a 219 bp coding region of the cDNA of a defensin from Trigonella foenumgraecum, designated as Tfgd2 using primers designed on the basis of a defensin, AlfAFP from Medicago sativa and reverse transcription-PCR. We have cloned the 701 bp genomic region of the defensin that comprised two exons and one long intron. The deduced amino acid sequence of Tfgd2 was similar to AlfAFP, except for two amino acid substitutions. It has 50% homology with the antifungal defensin Psd1 from Pisum sativum, whose NMR solution structure has been determined. The mature peptide has 45 amino acids, while the signal peptide comprised 27 amino acids. Southern analysis of the genomic DNA blot indicated that the defensins appear to be an oligo-gene family with at least two members in Trigonella. Purified peptide from Escherichia coli expression displayed inhibitory activity against broad-spectrum fungal pathogens, Rhizoctonia solani and Fusarium moniliforme.